Microprotractor



May 24, 1949. w. M. DETHLFs ETAL 2,471,099

MICROPROTRACTOR Filed Aug. 24, 1945 Zw" e A MZ/)mier le 9 4am( PatentedMay 24, 1949 MICROPROTRACTOR Walter M. Dethlefs, Santa Monica, and FredMinder, Los Angeles, Calif.

Application August 24, 1945, Serial No. .612,472

1 Claim. 1

The present invention relates to protractors, and is particularlyconcerned with a micro-protractor for the use of tool and die makers.

The primary object of the invention is to provide a device of the saidtype which will read not only in degrees, but to one-sixtieth oi adegree, or one minute in one operation.

Another object of the invention is to provide a micro-protractor ofsimpler and more compact construction than is disclosed by priordevices.

With the foregoing and other objects and advantages, the inventionconsists of the novel arrangement and construction of parts hereinafterdescribed and claimed.

In the accompanying drawings illustrating the invention:

Figure 1 is a top plan view of the invention with a portion of cover forgear housing broken away.

Figure 2 is a vertical transverse section thereof on line 2-2 of Figurel.

Figure 3 is a detail sectional view taken ver; tically through thebushing recess in the gear housing.

Like numerals designate the same parts of construction when referred toin the description anddrawings.

In its simplest and barest essentials, the invention consists of aprotractor, a straight-edge pivoted thereto, a frame, one edge of whichis aligned with the base of the protractor, rotary supplemental scalesand mechanism attached to the frame and adapted to coordinate saidscales and the protractor to accurately indicate the angle to minutes.

The frame Il consists of a flat rectangular ele` ment to which issuitably attached a gear housing 2 which is substantially semi-circularin contour and box-like with a removable cover 3. A rectangularcompartment 4 is set off from the interior of the housing approximatelyat the middle of its perimeter. In the main compartment of the housinga. gear-toothed sector 5, slightly more than a quadrant, is secured in ahorizontal position, at its center, on a vertical pin 6 which isrevolvably mounted in said housing centrally of the arcuate housing. Thelower end of pin B passes through the bottom of the housing and into arotatable, rectangular straight-edge l, to which it is secured fast by ahead set ush therein. The upper end of pin` 6 is provided with an indexpointer 8 adapted to be rotated by the pin.

On the cover 3 of the housing is an arcuate scale 9, of one 90 sectorwith 15 graduations.

2 These graduations are numbered from right to left in 6 steps, as forexample, 0-6-12-18-24, etc. The pin 6 is positioned in the center ofthis arcuate scale, and said scale is concentric with the gear-toothedsector 5. The base of the protractor is in alignment with an edge of theframe I.

Located in the compartment 4 is a worm gear Ill which is mounted on ashort revolvable shaft II journaled in the opposite side walls of thecompartment. This worm engages the toothed sector 5 and is adapted torotate same as desired. One end of said shaft is contained in a recess I2 in one wall of compartment Il of the housing and the shaft passes intothe recess through a circular opening leading from the interior ofcompartment 4 to recess I2. This circular opening I3 is larger than thediameter of the shaft I I', to permit a slight lateral movement of theshaft. A bushing I4 located in the rear of said recess is adapted toreceive the end of said shaft and provide a bearing therefor. Thisbushing is round except for flattened surfaces on opposite sides. Theseprevent the bushing from revolving with the shaft and also allow aslight movement of the worm toward and away from gear 5. A coiled springI5 maintains pressure on the said bushing to maintain the Worm inengagement and is confined in the recess by the threaded plug I6.

The opposite end of the shaft I I passes through a bearing in thecomplemental Wall of the compartment 4 and projects through .a sleeve I8fixedly mounted on the other side of said Wall and beyond the sleevethereof. To this projecting end is secured a thimble I6 which isprovided with a milled head I1 adapted to facilitate minute rotation ofthe shaft. The thimble I6 is cylindrical in form and includes a taperingportion I6c which loosely and slidably embraces the complemental end ofsleeve I8, and an enlarged portion I 6b intermediate the taperingportion I6c and the milled head Il. Sleeve I8 is provided on itsperiphery with a graduated scale numbered from 0 to 14, both inclusive,while the periphery of the enlarged portion I 6b of the thimble I6 isprovided with a graduated scale of 24 divisions, which is progressivelynumbered as follows, vis: 0, 15, 30, 45, 1; 15, 30, 45, 2; 15, '30, 45,3; 15, 30, 45, 4; 15, 30, 45, 5; 15, 30, 45 back to the initial 0. Thesegraduations are alternately three short ones, and a long one. Disposedabout the periphery of the tapering portion I6c of the thimble I9 are aplurality of scale lines s'o formed thereon as to coact with the scalelines of the scale on the sleeve I8 3 and the scale on the enlargedportion I6b of the thimble I6.

In operation, the straight-edge 'I is rotated from frame I through 90 bymeans of the worm and gear-toothed sector. These gears have a 60 to 1reduction, hence each revolution of the head I'I equals 6, the value ofeach gradation on the arcuate scale 9 of the protractor. The indexpointer will, therefore, on one revolution of I1 indicate the angle tothe nearest 6. Portion I6b of the thimble has 24 divisions to itsperipheral scale and each division represents one-quarter degree or 15minutes. On portion IGa are fifteen divisions in the scale, theseoccupying a space equal to that of fourteen divisions on portion IGb.The difference between the Width of one of the fifteen divisions onportion IBa and that of one of the fourteen divisions on portion IGZ)`is therefore one-fifteenth of a space on portion Ilia, at one time.Hence, the gradations on the portion IGa represent one-fifteenth of aquarter degree, or one minute. This is the Vernier principle used onmost micrometers reading in ten-thousandths.

Having thus described our invention, What We claim as new and desire tosecure by Lettersl Patent is:

A micro-protractor consisting of a frame provided With a housing and aremovable cover, a protractor with suitable arcuate scale to recorddegrees of an angle mounted on said cover with its base aligned on astraight-edge of the frame, an index-pointer mounted concentrically withsaid arcuate scale, a straight-edge mounted beneath said frameconcentrically with said arcuate scale 4 and adapted to rotate inconjunction with the index-pointer which is aligned therewith, arotatable vertical shaft mounted in said housing to which is securedsaid straight edge and index pointer, a gear toothed sector carried bysaid shaft, a horizontally disposed shaft mounted for limited lateralplay, a Worm on said last named shaft in meshing engagement with saidgear sector, a coiled spring adapted to bear on said last named shaftlaterally to maintain the Worm in mesh with said sector, a thimbleattached to the end o'f the last named shaft exteriorly of said housingand having a scale disposed about its periphery divided into one-quarterdegrees or fifteen minutes, a sleeve fixedly mounted on said frame incooperative association with said thimble and having a scale disposedabout its periphery, each division of which is equal to one-fifteenth ofthe circumference of the sleeve.

WALTER M. DETHLEFS. FRED MINDER.

REFERENCES CITED 'The following references are of record in the 25 fileof this patent:

UNITED STATES PATENTS

